Spectral characteristic investigation on complex of Ni (II) with captopril and its analytical application

Quantitative detection of captopril in urine by smartphone-assisted ratiometric fluorescence sensing platform

Captopril (CP) is a widely used antihypertensive drug. In this study, a smartphone-assisted sensing platform on the basis of ratiometric fluorescent test strips was developed, which can accomplish visualization for the quantitative detection of captopril. Ratiometric fluorescent probe was constructed from carbon dots (CDs) and gold nanoclusters (Au NCs). After adding Cu²⁺ to fluorescent probe, Cu²⁺ can complex the amino and carboxyl groups on the surface of Au NCs and aggregate Au NCs, which will quench the fluorescence of Au NCs. Compared with amino and carboxyl groups, -SH in CP has a higher affinity for Cu²⁺ and can capture Cu²⁺ to restore Au NCs fluorescence. In this process, CDs remained essentially unchanged as background fluorescence. As CP concentration increased, the fluorescence color showed a distinct change from blue to purple to orange. Based on this principle, a sensing platform combining smartphone and fluorescent test strips was constructed to visualize the quantitative detection of CP by RGB values. Under optimal conditions, the wide linear range of CP detection for both fluorescence spectrometer and smartphone paper-based sensing platform was 0.25-50 μM. The limits of detection were as low as 76 nM and 101.3 nM, respectively. Furthermore, it was implemented successfully for the detection of CP in urine. The satisfactory recoveries were 96.0-103.3% and 92.0-108.0% for fluorescence spectrometer and smartphone platform, respectively. This smartphone-assisted platform provided a new approach for visual detection of CP, which showed its great potential in bioanalytical assays.

Content determination of ampicillin by Ni(ii)-mediated UV-Vis spectrophotometry

Ampicillin could be degraded under alkaline conditions, of which the degradation products formed a complex with Ni²⁺ in a ratio of 2 : 1 in ammonium hydroxide. According to the study, it was found that there was a characteristic absorption peak at the wavelength of 269 nm, and the molar absorption coefficient and the stability constant of the complex was 4.28 × 10³ L mol⁻¹ cm⁻¹ and 5.95 × 10⁹, respectively. The linear relationship between the concentration and absorbance was favorable at the range of 17.47–69.88 μg mL⁻¹. The regression equation was calculated as A = 0.0124C + 0.0053. The R² was 0.9990 and the detection limit was 0.52 μg mL⁻¹. Thus, the Ni²⁺ complex-based ultraviolet spectrophotometry has been created as a new method for indirect determination of ampicillin, with recovery rates from 98.68 to 102.7%, and the relative standard deviation (RSD) is from 0.7% to 1.7%, when applied for determining the content of practical samples.

Ampicillin could be degraded under alkaline conditions, of which the degradation products formed a complex with Ni²⁺ in a ratio of 2 : 1 in ammonium hydroxide.

Development and Validation of an Automated Zone Fluidics-Based Sensor for In Vitro Dissolution Studies of Captopril Using Total Error Concept

In the present research, a zone fluidics-based automated sensor for the analysis of captopril in in vitro dissolution samples is reported. Captopril is reacted under flow conditions with Ni(II) (10 mmol L^-1) in alkaline medium (0.15% v/v NH₃) to form a stable derivate, which is monitored spectrophotometrically at 340 nm. The chemical and instrumental parameters were carefully investigated and optimized. The validation of the developed method was performed in the range of 5 to 120% of the expected maximum concentration using the accuracy profiles as a graphical decision-making tool. The β-expectation tolerance intervals did not exceed the acceptance criteria of ±10%, which means that 95% of future results will be encompassed in the defined bias limits. The variation of the relative bias ranged between -2.3% and 3.5% and the RSD values for repeatability and intermediate precision were lower than 2.3% in all cases. The limit of detection (LOD), and the lower and the upper limit of quantification (LLOQ, ULOQ) were satisfactory and found to be 1%, 5% and 120% (corresponding to 0.6, 2.78 and 66.67 μg mL^-1 in dissolution medium). The developed method was successfully applied for the analysis of captopril in dissolution tests of two commercially available batches.

Circular Dichroism Spectroscopy: A Facile Approach for Quantitative Analysis of Captopril and Study of Its Degradation

Simple and selective zero- and second-order derivative circular dichroism (CD) spectroscopic methods have been designed for the assay of captopril in commercially available dosage forms. A normal CD spectroscopic scan (zero order) exhibits a negative band at 208 nm (method A) in distilled water. The calibration curve shows a linear response over the concentration range of 10-80 μg mL^-1. The second-order derivative (D2) CD spectrum shows one positive band at 208 nm (method B) and one negative band at 225 nm (method C). Linear calibration curves were obtained in the concentration range of 10-70 μg mL^-1 for both the methods (B and C). The detection limits were found to be 1.26, 1.48, and 2.38 μg mL^-1 for methods A, B, and C, respectively. The study under stressed acidic, basic, and oxidative conditions showed the degradation of captopril. The proposed methods were validated as per ICH guidelines. All the proposed methods were compared with the reference method to demonstrate its suitability for quality control of captopril in its dosage forms.